Develop normal, preneoplastic, and malignant human breast cell lines. After establishment in culture, characterize the cell lines to establish their identity as human mammary epithelial cells. Employ karyotyping, biochemical testing for breast cell products such as casein and electron microscopic confirmation of an epithelial cell morphology. Determine cell culture characteristics of the cell lines, especially with regard to properties such as saturation densities which correlate well with malignancy in vivo. Detect tumor virus particles in the cell lines using techniques such as electron microscopy, density gradient centrifugation, and others. Induce virus particles or products from the human breast cell line using hormones, halogenated pyramidines, at various incubation temperatures.